Conventionally, in the fields of chemical analysis, biochemical analysis, and the like, an SPR sensor (Surface Plasmon Resonance) sensor including an optical fiber has been used.
In the SPR sensor including the optical fiber, a metal thin film is formed on the outer peripheral surface of the tip portion of the optical fiber, while an analysis sample is fixed thereto, and light is introduced into the optical fiber. Of the introduced light, light at a specified wavelength causes surface plasmon resonance in the metal thin film to attenuate the light intensity thereof.
In such an SPR sensor, the wavelength which causes the surface plasmon resonance normally differs depending on the refractive index of the analysis sample fixed to the optical fiber.
Therefore, if the wavelength at which the light intensity attenuates after the occurrence of the surface plasmon resonance is measured, the wavelength that has caused the surface plasmon resonance can be specified. Also, if the wavelength at which the attenuation occurs has changed and is detected, it is possible to confirm that the wavelength which causes the surface plasmon resonance has changed. This allows a change in the refractive index of the analysis sample to be confirmed.
Consequently, such an SPR sensor can be used for various chemical analyses and biochemical analyses such as, e.g., measurement of the concentration of a sample and detection of an immune reaction.
For example, when the sample is a solution, the refractive index of the sample (solution) depends on the concentration of the solution. Accordingly, in the SPR sensor in which the sample (solution) is brought into contact with a metal thin film, by measuring the refractive index of the sample (solution), the concentration of the sample can be detected and, by also confirming that the refractive index thereof has changed, it can be confirmed that the concentration of the sample (solution) has changed.
In the analysis of an immune reaction, e.g., an antibody is fixed onto the metal thin film of the optical fiber in the SPR sensor via a dielectric film and a specimen is brought into contact with the antibody, while surface plasmon resonance is caused. At this time, if an immune reaction occurs between the antibody and the specimen, the refractive index of the sample changes. Therefore, by confirming that there is a change between the refractive indices of the sample before and after the contact between the antibody and the specimen, it can be determined that the immune reaction has occurred between the antibody and the specimen.
However, in an SPR sensor including such an optical fiber, the tip portion of the optical fiber has a minute cylindrical shape resulting in the problem that it is difficult to form a metal thin film and fix an analysis sample.
To solve the problem, an SPR sensor cell has been proposed which includes, e.g., a core through which light is transmitted and a clad covering the core. At a predetermined position in the clad, a through hole is formed to reach the surface of the core, and a metal thin film is formed on the surface of the core at a position corresponding to the through hole (see, e.g., Patent Document 1 shown below).
The SPR sensor cell allows easy formation of the metal thin film for causing surface plasmon resonance on the surface of the core and easy fixation of the analysis sample to the surface thereof.